Methods of reducing power in programmable logic devices using low voltage swing for routing signals

ABSTRACT

Reduced voltage swing signal path circuitry is provided that lowers the internal signaling power consumption of the interconnection resources of a programmable logic device. The reduced voltage swing signal path circuitry includes a reversed routing driver circuitry to limit the voltage range of the output signal of the driver circuitry.

BACKGROUND OF THE INVENTION

The present invention relates generally to programmable logic devices (PLDs), and more particularly to reducing power consumption in such devices.

It should be noted that the term PLD as used herein is intended to cover the broad space of programmable logic. This includes devices commonly known as CPLDs (Complex Programmable Logic Devices) such as MAX 7000® from Altera Corporation of San Jose, Calif., FPGAs (Field Programmable Gate Arrays) such as Stratix® from Altera, or Structured ASICs (metal programmable logic) such as Hardcopy® from Altera.

Examples of known programmable logic devices are shown in Cliff et al. U.S. Pat. Nos. 5,909,126 and 5,963,049, which are hereby incorporated by reference herein in their entireties. PLDs typically include large numbers of regions of programmable logic and other operational resources such as memory, input/output circuits, etc., that are selectively interconnectable via programmable interconnection resources on the device. For example, each region of programmable logic on a PLD may be programmable to perform any of several relatively simple logic functions on several input signals applied to that region in order to produce one or more output signals indicative of the result of performing the selected logic function(s) on the input signals. The interconnection resources are programmable to convey voltage signals (ranging from a ground voltage V_(SS) (e.g., a “LOW” voltage signal) to a source voltage V_(CC) (e.g., a “HIGH” voltage signal) to, from, and between the logic regions in any of a wide variety of patterns or configurations. For example, the interconnection resources may be used to concatenate several logic regions so that much more complex logic tasks can be performed than any one logic region can perform.

It is typical to use a single conductor for each individual interconnection pathway or path segment in PLDs. Single or multiple MOS pass gates (controlled by programmable memory elements or circuits on the PLD) are used for selectively interconnecting each conductor to other conductors to provide various signal routings through the interconnection resources of the device.

The operation of a typical single-transistor pass gate may be succinctly illustrated by a description of an NMOS pass gate (analogous principles of operation, as understood by one skilled in the art, would apply for a PMOS pass gate). Depending on whether the potential difference between its gate terminal, V_(GATE), and its source terminal, V_(SOURCE), exceeds the threshold voltage, V_(T), an NMOS pass gate acts as an “open” or a “closed” switch. (As is well-known in the art, there is no physical difference between the “source” and “drain” terminals of a MOS device.) When V_(GATE)−V_(SOURCE) is less than V_(T), the NMOS pass gate is in the “cutoff” state, thereby acting as an “open” switch; when V_(GATE)−V_(SOURCE) is greater than V_(T), the NMOS pass gate is in the conduction state, thereby acting as a “closed” switch.

As is well-known in the art, V_(T) is not a discrete value for a MOS transistor; it may be considered a range of values that is influenced by a variety of second-order effects, such as substrate bias and subthreshold conduction. However, in order to simplify the illustration of the principles of the present invention, V_(T) will be discussed herein as if it is a discrete value rather than a range of values.

With the current trend in scaling down device geometries (e.g., 0.18 μm process down to 0.13 μm, 90 nm, 65 nm, or lower) and the consequent use of ever-lower operating voltages (e.g., supply voltages, bias voltages, etc.), which are nearing levels comparable to V_(T), the ability of transistor pass gate structures to function at relatively high speeds while at the same time minimizing leakage current is a difficult design hurdle to overcome.

Moreover, this trend of smaller device geometries and consequent use of lower operating voltages is creating a design tradeoff between speed (e.g., response time for the pass gate transistor to turn ON) and leakage current (e.g., the current that passes through the pass gate transistor when turned OFF) that was not previously experienced with larger device geometries and the consequent use of higher operating voltages. That is, if conventional design techniques are applied to smaller device geometries, high speed pass gate operation is accompanied with high leakage current, whereas low leakage current is accompanied with low speed pass gate operation. High leakage current is undesirable because it results in excess heat, power loss, and poorer performance.

Another problem associated with shrinking geometries is the consequent use of lower operating voltages. This lower operating voltage is typically a nominal voltage supplied to the device, and may be insufficient for certain circuitry, such as configurable memory cells (e.g., SRAM) within the device, to operate properly. For example, as the supply voltage decreases, the soft-error-rate increases because the critical charge needed to flip the cells (from one logic state to another) is reduced.

A large percentage of a device's power is consumed by the capacitive charging and discharging of the interconnection conductors. At lower operating voltages, the V_(T) drop of NMOS pass gates becomes a more significant fraction or percentage of the operating voltage. This can lead to several problems in conventional PLD interconnection circuitry. For example, signaling slows down and the circuitry becomes increasingly susceptible to capacitive cross-talk between parallel conductors.

Accordingly, it would be desirable to provide improved techniques, systems, and methods for lowering the internal signaling power consumption of a programmable logic device.

SUMMARY OF THE INVENTION

In accordance with the present invention, improved techniques, systems, and methods for lowering the internal signaling power consumption of a programmable logic device are provided.

The present invention achieves lower power consumption of a programmable logic device by reducing the total amount of charge that needs to be routed through the interconnection resources. Driver circuitry is provided for driving a routing signal from source operational circuitry to receiver circuitry via an interconnection conductor. The driver circuitry limits the routing signal from being driven all the way to the extremes of the programmable logic device's power supply.

In accordance with the present invention, there is provided a programmable logic device that includes first operational circuitry, second operational circuitry, routing driver circuitry coupled to an output signal of the first operational circuitry, routing receiver circuitry coupled to an input of the second operational circuitry, and an interconnection conductor that extends from the driver circuitry to the receiver circuitry. The driver circuitry is configured to drive a routing signal onto the interconnection conductor such that the voltage swing of the routing signal is less than the voltage swing of the output signal of the first operational circuitry.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages of the invention will be more apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:

FIG. 1 is a simplified schematic block diagram of a representative portion of an illustrative PLD which can be constructed in accordance with the present invention;

FIG. 2 is a simplified schematic block diagram of illustrative signaling circuitry in accordance with the present invention;

FIG. 3 is a simplified schematic block diagram of other illustrative signaling circuitry in accordance with the present invention;

FIG. 4 is a simplified schematic block diagram of still other illustrative signaling circuitry in accordance with the present invention;

FIG. 5 is a more detailed schematic diagram of prior art circuitries of the type shown in FIGS. 2-4;

FIG. 6 is a detailed schematic diagram, similar to the diagram of FIG. 5, of an illustrative embodiment of possible modifications of portions of the circuitries of FIG. 5 in accordance with the present invention;

FIG. 7 is a detailed schematic diagram, similar to the diagrams of FIGS. 5 and 6, of a second illustrative embodiment of possible modifications of portions of the circuitries of FIG. 5 in accordance with the present invention; and

FIG. 8 is a simplified block diagram of an illustrative system employing a programmable logic device having signaling circuitry in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a representative portion of an illustrative PLD 10 that can be constructed in accordance with the invention. PLD 10 includes regions 20 of input/output (I/O) circuitry, regions 30 of programmable logic, and regions 40 of user-accessible memory. Other types of operational circuitry (e.g., microprocessor circuitry) may also be included on PLD 10. For example, such other circuitry may be in addition to what is shown in FIG. 1, or it may take the place of some of regions 40. Interconnection resources are also included on PLD 10. These resources include horizontal interconnection resources 50, vertical interconnection resources 60, region feeding resources 70, region output resources 80, and I/O serving resources 90. (Single lines in FIG. 1 may represent multiple, substantially parallel conductors.) The interconnection resources also include programmable connections between the various types of other interconnection resources. These programmable connections are represented by the circles or other shapes indicated by reference numbers 100 at the intersections of possibly connectable conductors. Connections 100 can be relatively simple and conventional programmable logic connectors (PLCs) controlled by conventional programmable function control elements (FCEs).

The interconnection resources are programmable to connect substantially any signal source to substantially any signal destination in PLD 10. As just one example of this, a signal from upper left I/O region 20 can be routed through the interconnection resources to the lowest input 70 to the logic region 30 nearest the center of FIG. 1. Various ones of resources 50, 60, 90, and 100 are used to provide such routing. As another example, an output signal of the upper left logic region 30 can be routed to the uppermost input 70 of the logic region 30 nearest the center of FIG. 1. Various ones of resources 50, 60, 80, and 100 are used to provide such routing.

FIG. 2 shows one illustrative signaling path arrangement 110 on PLD 10 (FIG. 1) in accordance with this invention. The source of the signal in path 110 can be any of an I/O region 20, a logic region 30, a memory region 40, a programmable interconnection 100, or any other signal source on PLD 10. A source signal 112 produced by source 20/30/40/100 is applied to routing driver circuitry 200. Driver circuitry 200 drives source signal 112 onto a conductor that can be any of types 50, 60, 70, 80, or 90, or any other type of conductor used on PLD 10, as routing signal 113. The conductor 50/60/70/80/90 extending from driver circuitry 200 runs to routing receiver circuitry 300. Receiver circuitry 300 passes routing signal 113 on conductor 50/60/70/80/90 as destination signal 114 for application to the associated signal destination, which (like the signal source) can be any of an I/O region 20, a logic region 30, a memory region 40, a programmable interconnection 100, or any other signal destination on PLD 10. Details of illustrative constructions of circuits 200 and 300 in accordance with this invention are provided later in this specification.

Another illustrative signaling path arrangement 120 on PLD 10 (FIG. 1) in accordance with the invention is shown in FIG. 3. The signal source element 20/30/40/100, the routing driver circuitry 200, and the output conductor 50/60/70/80/90 of circuitry 200 can be similar to the corresponding elements in FIG. 2. The “horizontal” conductor 50/60/70/80/90 is connected to the input gate of each of two (or more) switching circuits 106 a and 106 b. The input gate of each of circuits 106 is controlled by an associated programmable function control element (FCE) 102 a/102 b. If it is desired for a circuit 106 to input and pass on the signal on the horizontal conductor 50/60/70/80/90, the FCE 102 associated with that circuit 106 is programmed to enable the input gate of that circuit. The circuit 106 can then receive and pass on to the associated “vertical” conductor 50/60/70/80/90 the routing signal 113 on the horizontal conductor 50/60/70/80/90. Each routing receiver circuitry 300 a or 300 b that thus receives routing signal 113 passes that signal as a destination signal 114 for use by the associated signal destination element 20/30/40/100. Each receiver circuitry 300 in FIG. 3 can be similar to circuitry 300 in FIG. 2, and the signal destination elements 20/30/40/100 in FIG. 3 can each be similar to the signal destination element in FIG. 2.

Still another illustrative signaling path arrangement 130 on PLD 10 (FIG. 1) in accordance with the invention is shown in FIG. 4. Each signal source element 20/30/40/100 in FIG. 4 can be similar to the signal source elements in FIGS. 2 and 3. Each routing driver circuitry 200 in FIG. 4 can be similar to driver circuitry 200 in FIGS. 2 and 3, except that in FIG. 4 each driver circuitry 200 is shown having output gates controlled by FCEs 202. Thus each driver circuitry 200 in FIG. 4 outputs a routing signal 113 only when the associated output gates are enabled by the associated FCE 202. In this way “vertical” interconnection conductor 50/60/70/80/90 can be driven by either of two (or more) driver circuitries 200.

Each routing receiver circuitry 300 in FIG. 4 can be similar to receiver circuitry 300 in FIGS. 2 and 3, except that in FIG. 4 each receiver circuitry 300 is shown having an input gate controlled by FCEs 302. Thus each receiver circuitry 300 receives routing signals 113 and passes destination signals 114 from vertical conductor 50/60/70/80/90 only if its associated input gate is enabled by the associated FCE 302. Each signal destination element 20/30/40/100 in FIG. 4 can be similar to the signal destination elements in FIGS. 2 and 3.

Switching circuit 106 in FIG. 4 is similar to any of the switching circuits 106 in FIG. 3, except that in FIG. 4 circuit 106 additionally has an output gate controlled by FCE 104. Thus circuit 106 in FIG. 4 outputs a signal only if its output gate is enabled by the associated FCE 104.

From the illustrative examples shown in FIGS. 2-4, it will be understood how any or all of the interconnection resources 50/60/70/80/90 in illustrative PLD 10 (FIG. 1) can be signaling or routing circuitry in accordance with this invention.

Circuitry and methods according to the invention provide a system that lowers the internal signaling power consumption of a programmable logic device. In particular, circuitry according to the invention achieves lower power consumption of a programmable logic device by reducing the total amount of charge that needs to be routed through the various signaling paths of the device. Typically, operating voltage is the supply voltage being supplied to the signal path circuitry of the device, and is commonly referred to as V_(CC).

Signal path circuitry according to the invention translates voltages that are lower than the source voltage by using “reversed” routing driver circuitry. The reversed routing driver circuitry limits the range of its output in the signal path circuitry to prevent the routed signal from being driven all the way to the extremes of the device's power supply (i.e., Ground to V_(CC)). For example, in one embodiment of routing driver circuitry of the invention, a HIGH input source signal (e.g., V_(CC)) is driven as a routing signal to an output voltage (e.g., V_(CCP)=V_(CC)−V_(TN)) lower than the voltage of the input source signal. Likewise, a LOW input source signal (e.g., V_(SS)) is driven as a routing signal to an output voltage (e.g., V_(SSP)=V_(TP)) higher than the voltage of the input source signal. In this case, the routing driver circuitry limits the range of its output voltage (i.e., reduces the voltage swing) on the interconnection resources in the signal path circuitry to lower power consumption on the PLD. The signal path circuitry of the invention may also include routing receiver circuitry having a mixture of pass gates and latch/buffer circuitry to restore the routing signal to full-rail as a destination signal.

FIG. 5 shows an example of a prior art V_(CC) to V_(SS) voltage level signal path circuitry 140. Conventional signal path circuitry 140 includes routing driver circuitry 200 a and routing receiving circuitry 300 a. (Reference numbers with letter suffixes like 200 a, 200 b, 300 a, 300 b, etc. are used in FIGS. 5-7 to help distinguish different illustrative embodiments of generally similar circuitries. In earlier FIGS., similar reference numbers with letter suffixes are used for a different purpose (i.e., to distinguish different instances of the same circuitry). It is not to be understood, for example, that the circuitry 300 a in FIG. 4 can only be constructed like embodiment 300 a in FIG. 5. Rather, any of the embodiments 300 a-c shown respectively in FIGS. 5, 6, and 7 can be used for circuitry 300 a in FIG. 4, or indeed for any instance of a routing receiver circuitry 300 in any of FIGS. 2-4.)

Each signal source element 20/30/40/100 in FIG. 5 can be similar to the signal source elements in FIGS. 2-4. The source of the signal in the signal path of circuitry 140 can be any of an I/O region 20, a logic region 30, a memory region 40, a programmable interconnection 100, or any other signal source on PLD 10; A source signal 112 a produced by source 20/30/40/100 is applied to routing driver circuitry 200 a. Driver circuitry 200 a drives source signal 112 a onto a conductor that can be any of types 50, 60, 70, 80, or 90 or any other type of conductor used on PLD 10. The conductor 50/60/70/80/90 extending from driver circuitry 200 a runs to routing receiver circuitry 300 a. Each signal destination element 20/30/40/100 in FIG. 5 can be similar to the signal destination elements in FIGS. 2-4. Receiver circuitry 300 a passes routing signal 113 a on conductor 50/60/70/80/90 as destination signal 114 a for application to the associated signal destination, which (like the signal source) can be any of an I/O region 20, a logic region 30, a memory region 40, a programmable interconnection 100, or any other signal destination on PLD 10.

In FIG. 5, source signal 112 a from the associated signal source 20/30/40/100 is applied to the input terminal 212 a of routing driver circuitry 200 a. V_(CC) is a source of power or logic 1 voltage or potential. V_(SS) is ground or logic 0 voltage or potential. Element 214 a is a PMOS transistor or gate. Elements 216 a and 218 a are NMOS transistors or gates. Element 202 a is an FCE (described earlier). Terminal 220 a is the output terminal of routing driver circuitry 200 a. Elements 202 a and 218 a are all optional and can be omitted for any circuitry 200 a that is the sole drive for the associated interconnection conductor 50/60/70/80/90.

Node A, which is formed between the gates of PMOS transistor 214 a and NMOS transistor 216 a, is connected to input terminal 212 a of driver circuitry 200 a. Node B, which is formed between the drain of PMOS transistor 214 a and the source of NMOS transistor 216 a, is connected to output terminal 220 a of circuitry 200 a (optional transistor 218 a may be coupled between node B and terminal 220 a if needed). The source of PMOS transistor 214 a is coupled to V_(CC) and the drain of NMOS transistor 216 a is coupled to V_(SS).

It will be understood that the drain and source orientation of the transistors described herein with respect to driver circuitry 200 a is not intended to be limiting, but merely illustrative of one way such transistors can be constructed. Therefore, the terms “source” and “drain” are to be interpreted in their broadest sense.

Operation of the prior art driver circuitry 200 a shown in FIG. 5 is as follows. (This description assumes that if optional elements 202 a and 218 a are present, then FCE 202 a is programmed to turn ON transistor 218 a.) When source signal 112 a is HIGH (i.e., equal to V_(CC)), NMOS transistor 216 a is ON and PMOS transistor 214 a is OFF. When NMOS transistor 216 a is ON, a direct path exists through transistor 216 a, between V_(SS) and node B. Therefore, output terminal 220 a of driver circuitry 200 a passes low signal V_(SS) as routing signal 113 a to interconnection conductor 50/60/70/80/90. On the other hand, when source signal 112 a is LOW (i.e., equal to V_(SS)) PMOS transistor 214 a is ON and NMOS transistor 216 a is OFF. When PMOS transistor 214 a is ON, a direct path exists through transistor 214 a, between V_(CC) and node B. Therefore, output terminal 220 a of driver circuitry 200 a passes high signal V_(CC) as routing signal 113 a to interconnection conductor 50/60/70/80/90. The routing driver circuitry 200 a thus clearly functions as an inverter. The high and low output levels at node B (and thus output terminal 220 a) equal V_(CC) and V_(SS), respectively. In other words, the voltage swing of routing driver circuitry 200 a is equal to the supply voltage. The range of output voltages driven by routing driver circuitry 200 a as routing signal 113 a varies all the way between V_(CC) and V_(SS).

The routing signal 113 a driven onto interconnection conductor 50/60/70/80/90 is applied to routing receiver circuitry 300 a. Receiver circuitry 300 a passes routing signal 113 a on conductor 50/60/70/80/90 as destination signal 114 a for application to the associated signal destination, which (like the signal source) can be any of an I/O region 20, a logic region 30, a memory region 40, a programmable interconnection 100, or any other signal destination on PLD 10, similar to the signal destination elements in FIGS. 2-4.

In FIG. 5, routing signal 113 a from the interconnection conductor 50/60/70/80/90 is applied to the input terminal 312 a of prior art routing receiver circuitry 300 a. V_(CC) is a source of power or logic 1 voltage or potential. V_(SS) is ground or logic 0 voltage or potential. Elements 314 a and 315 a are NMOS transistors or gates. Elements 316 a and 317 a are PMOS transistors or gates. Elements 301 a and 302 a are FCEs. Element 303 a is an active global signal (i.e., a power-up latch reset signal) that is LOW at power-up. Elements 318 a and 319 a are inverters. Terminal 320 a is the output terminal of routing receiver circuitry 300 a. NMOS transistor 315 a and FCE 302 a together, and in combination with optional NMOS transistor 314 a and FCE 301 a, form a pass gate. Inverter 318 a in combination with PMOS transistor 317 a forms a common half-latch. PMOS transistor 316 a in combination with power-up signal 303 a forms a “pull-up” circuit.

Node C is formed between the drain of NMOS “pass gate” transistor 315 a and the drains of PMOS transistors 316 a and 317 a. The source of NMOS pass gate transistor 315 a is coupled to input terminal 312 a (optional NMOS pass gate transistor 314 a may be coupled between terminal 312 a and the source of NMOS pass gate transistor 315 a at node (C) if desired). Node D is formed between the gate of PMOS transistor 317 a and the output of inverter 318 a. Node E, which is formed at the output of inverter 319 a, is connected to output terminal 320 a of circuitry 300 a. The gate of NMOS transistor 314 a is coupled to FCE 301 a and the gate of NMOS transistor 315 a is coupled to FCE 302 a. The gate of PMOS transistor 316 a is coupled to power-up signal 303 a while the source of each of PMOS transistors 316 a and 317 a is coupled to V_(CC).

It will be understood that the drain and source orientation of the transistors described herein with respect to routing receiver circuitry 300 a is not intended to be limiting, but merely illustrative of one way such transistors can be constructed. Therefore, the terms “source” and “drain” are to be interpreted in their broadest sense.

Operation of the conventional receiver circuitry 300 a shown in FIG. 5 is as follows. (This description assumes that if optional elements 301 a and 314 a are present, then FCE 301 a is programmed to turn ON transistor 314 a.) When routing signal 113 a is HIGH (i.e., source signal 112 a is equal to V_(SS)), NMOS pass gates 314 a and 315 a pass HIGH routing signal 113 a if FCEs 301 a and 302 a are programmed to turn transistors 314 a and 315 a ON, respectively. If one or both of FCEs 301 a and FCE 302 a is not programmed to turn ON its respective pass transistor (i.e., if either or both of FCEs 301 a and 302 a are LOW), then routing signal 113 a is not being passed to node C of receiver circuitry 300 a and, therefore, node C is floating. In that instance, which at least occurs at power-up of the programmable logic device on which signal path circuitry 140 is contained when all FCEs are cleared (i.e., are LOW), power-up signal 303 a of the pull-up circuit turns PMOS transistor 316 a ON, thereby setting node C HIGH by passing V_(CC) through transistor 316 a. In all other cases, when both of FCEs 301 a and 302 a are programmed to turn transistors 314 a and 315 a ON, respectively, the pull-up circuit becomes inactive and node C is driven by routing signal 113 a via transistor 315 a (and transistor 314 a if provided).

Once routing signal 113 a is passed by one or both of the NMOS pass gates to node C (or once node C is set high by the pull-up circuit), the common half-latch circuitry formed by PMOS transistor 317 a and inverter 318 a holds the signal at node D to V_(CC) or V_(SS), whichever is substantially the inverse of the signal at node C. Therefore, whatever current leakage occurs due to the pass gate(s), the half-latch will set the signal at node D equal to one of the full-rail values of the supply voltage (i.e., V_(CC) or V_(SS)). Inverter 319 a is also provided to hold the signal at node E to V_(CC) or V_(SS), whichever is substantially the inverse of the signal at node D. Therefore, whenever FCE 301 a is programmed to turn ON transistor 314 a and FCE 302 a is programmed to turn ON transistor 315 a, output terminal 320 a of receiver circuitry 300 a passes HIGH signal V_(CC) as destination signal 114 a to destination circuitry 20/30/40/100 when source signal 112 a is LOW, and thus routing signal 113 a at node B is HIGH. Also, whenever FCE 301 a is programmed to turn ON transistor 314 a and FCE 302 a is programmed to turn ON transistor 315 a, output terminal 320 a of receiver circuitry 300 a passes LOW signal V_(SS) as destination signal 114 a to destination circuitry 20/30/40/100 when source signal 112 a is HIGH, and thus routing signal 113 a at node B is LOW. Yet, whenever one or both of FCEs 301 a and 302 a are not programmed to turn ON respective transistors 314 a and 315 a, output terminal 320 a of receiver circuitry 300 a passes HIGH signal V_(CC) as destination signal 114 a to destination circuitry 20/30/40/100 due to the pull-up circuitry of receiver circuitry 300 a and regardless of source signal 112 a.

Therefore, prior art signal path circuitry 140 drives a V_(CC) source signal 112 a via driver circuitry 200 a as a V_(SS) routing signal 113 a along interconnection conductor 50/60/70/80/90, and passes the V_(SS) routing signal 113 a to source destination circuitry 20/30/40/100 as a V_(SS) destination signal 114 a. Similarly, prior art signal path circuitry 140 drives a V_(SS) source signal 112 a via driver circuitry 200 a as a V_(CC) routing signal 113 a along interconnection conductor 50/60/70/80/90, and passes the V_(CC) routing signal 113 a to source destination circuitry 20/30/40/100 as a V_(CC) destination signal 114 a. Thus, the voltage swing of routing signal 113 a driven along interconnection conductor 50/60/70/80/90 is equal to the supply voltage of signal path circuitry 140 (i.e., V_(CC) to V_(SS)).

FIG. 6 shows a detailed schematic diagram of a reduced voltage swing signal path circuitry 150 according to the present invention. Signal path circuitry 150 includes “reversed” routing driver circuitry 200 b and routing receiver circuitry 300 b.

Each signal source element 20/30/40/100 in FIG. 6 can be similar to the signal source elements in FIGS. 2-5. The source of the signal in the signal path of circuitry 150 can be any of an I/O region 20, a logic region 30, a memory region 40, a programmable interconnection 100, or any other signal source on PLD 10. A source signal 112 b produced by source 20/30/40/100 is applied to routing driver circuitry 200 b. Driver circuitry 200 b drives source signal 112 b onto a conductor that can be any of types 50, 60, 70, 80, or 90 or any other type of conductor used on PLD 10. The conductor 50/60/70/80/90 extending from driver circuitry 200 b runs to routing receiver circuitry 300 b. Each signal destination element 20/30/40/100 in FIG. 6 can be similar to the signal destination elements in FIGS. 2-5. Receiver circuitry 300 b passes the signal on conductor 50/60/70/80/90 as destination signal 114 b for application to the associated signal destination, which (like the signal source) can be any of an I/O region 20, a logic region 30, a memory region 40, a programmable interconnection 100, or any other signal destination on PLD 10.

In FIG. 6, source signal 112 b from the associated signal source 20/30/40/100 is applied to the input terminal 212 b of routing driver circuitry 200 b. V_(CC) is a source of power or logic 1 voltage or potential. V_(SS) is ground or logic 0 voltage or potential. Element 214 b is a PMOS transistor or gate. Elements 216 b and 218 b are NMOS transistors or gates. Element 202 b is an FCE (described earlier). Terminal 220 b is the output terminal of routing driver circuitry 200 b. Elements 202 b and 218 b are all optional and can be omitted for any circuitry 200 b that is the sole drive for the associated interconnection conductor 50/60/70/80/90.

Node A′, which is formed between the gates of PMOS transistor 214 b and NMOS transistor 216 b, is connected to input terminal 212 b of driver circuitry 200 b. Node B′, which is formed between the source of PMOS transistor 214 b and the drain of NMOS transistor 216 b, is connected to output terminal 220 b of circuitry 200 b (optional transistor 218 b may be coupled between node B′ and terminal 220 b if needed). The drain of PMOS transistor 214 is coupled to V_(SS) and the source of NMOS transistor 216 is coupled to V_(CC).

It will be understood that the drain and source orientation of the transistors described herein with respect to driver circuitry 200 b is not intended to be limiting, but merely illustrative of one way such transistors can be constructed. Therefore, the terms “source” and “drain” are to be interpreted in their broadest sense.

Operation of driver circuitry 200 b shown in FIG. 6 is as follows. (This description assumes that if optional elements 202 b and 218 b are present, then FCE 202 b is programmed to turn ON transistor 218 b.) When source signal 112 b is HIGH (i.e., equal to V_(CC)), NMOS transistor 216 b is ON and PMOS transistor 214 b is OFF. When NMOS transistor 216 b is ON, a direct path exists through transistor 216 b, between V_(CC) and node B′. Therefore, output terminal 220 b of driver circuitry 200 b passes reduced-HIGH signal V_(CCN) (i.e., V_(CC)−V_(TN)) as routing signal 113 b to interconnection conductor 50/60/70/80/90. On the other hand, when source signal 112 b is LOW (i.e., equal to V_(SS)) PMOS transistor 214 b is ON and NMOS transistor 216 b is OFF. When PMOS transistor 214 b is ON, a direct path exists through transistor 214 b, between V_(SS) and node B′. Therefore, output terminal 220 b of driver circuitry 200 b passes increased-LOW signal V_(SSP) (i.e., V_(SS)+V_(TP)) as routing signal 113 b to interconnection conductor 50/60/70/80/90. The routing driver circuitry 200 b thus clearly functions as an inverter with a reduced voltage swing. The “HIGH” and “LOW” output levels at node B′ (and thus output terminal 220 b) equal V_(CCN) (i.e., V_(CC)−V_(TN)) and V_(SSP) (i.e., V_(SS)+V_(TP)), respectively. In other words, the voltage swing of routing driver circuitry 200 b is not equal to the supply voltage. Unlike in prior art driver circuitry 200 a of FIG. 5, the range of output voltages driven by routing driver circuitry 200 b as routing signal 113 b of FIG. 6 cannot vary all the way between V_(CC) and V_(SS).

The routing signal 113 b driven onto interconnection conductor 50/60/70/80/90 is applied to routing receiver circuitry 300 b. Receiver circuitry 300 b passes routing signal 113 b on conductor 50/60/70/80/90 as destination signal 114 b for application to the associated signal destination, which (like the signal source) can be any of an I/O region 20, a logic region 30, a memory region 40, a programmable interconnection 100, or any other signal destination on PLD 10, similar to the signal destination elements in FIGS. 2-5.

In FIG. 6, routing signal 113 b from the interconnection conductor 50/60/70/80/90 is applied to the input terminal 312 b of routing receiver circuitry 300 b. V_(CC) is a source of power or logic 1 voltage or potential. V_(SS) is ground or logic 0 voltage or potential. Elements 314 b and 317 b are NMOS transistors or gates and elements 315 b and 316 b are PMOS transistors or gates. Elements 301 b and 302 b are FCEs. Elements 303 b and 304 b are active global signals (i.e., power-up latch reset signals) that are LOW and HIGH at power-up, respectively. Elements 313 b, 318 b, and 319 b are inverters. Terminal 320 b is the output terminal of routing receiver circuitry 300 b. NMOS transistor 314 b and FCE 301 b, together and in combination with PMOS transistor 315 b and FCE 302 b, form pass gate circuitry. (It should be noted that the order of NMOS transistor 314 b and PMOS transistor 315 b may be switched, and these transistors may protect routing signal 113 b from being brought to full-rail at node C′ by the full latch of circuitry 300 b). Inverter 313 b in combination with inverter 318 b form a common full-latch. PMOS transistor 316 b in combination with power-up signal 303 b forms a “pull-up” circuit, while NMOS transistor 317 b in combination with power-up signal 304 b forms a “pull-down” circuit. It should be noted that only one of the pull-up device or the pull-down circuit is necessary.

Node C′ is formed between the drains of PMOS transistors 315 b and 316 b, the source of NMOS transistor 317 b, the output of inverter 313 b, and the input of inverter 318 b. The source of PMOS pass gate transistor 315 b is coupled to the drain of NMOS pass gate 314 b. The source of NMOS pass gate 314 b is coupled to input terminal 312 b. Node D′ is formed between the inputs of inverters 313 b and 319 b, and the output of inverter 318 b. Node E′, which is formed at the output of inverter 319 b, is connected to output terminal 320 b of circuitry 300 b. The gate of NMOS transistor 314 b is coupled to FCE 301 b and the gate of PMOS transistor 315 b is coupled to FCE 302 b. The gate of PMOS transistor 316 b is coupled to power-up signal 303 b, while the gate of NMOS transistor 317 b is coupled to power-up signal 304 b. The source of PMOS transistor 316 b is coupled to V_(CC), while the drain of NMOS transistor 317 b is coupled to V_(SS).

It will be understood that the drain and source orientation of the transistors described herein with respect to routing receiver circuitry 300 b is not intended to be limiting, but merely illustrative of one way such transistors can be constructed. Therefore, the terms “source” and “drain” are to be interpreted in their broadest sense.

Operation of receiver circuitry 300 b shown in FIG. 6 is as follows. When routing signal 113 b is a reduced-HIGH signal V_(CCN) (i.e., source signal 112 b is equal to V_(CC)), pass gates 314 b and 315 b pass reduced-HIGH routing signal 113 b if FCEs 301 b and 302 b are programmed to turn ON transistors 314 b and 315 b, respectively. If either or both of FCEs 301 b and 302 b is not programmed to turn ON its respective pass transistor (i.e., if FCE 301 b is LOW and/or FCE 302 b is HIGH), then routing signal 113 b is not being driven to node C′ of receiver circuitry 300 b and, therefore, node C′ is floating. In that instance, which at least occurs at power-up of the programmable logic device on which circuitry 150 is contained, power-up signal 303 b of the pull-up circuit may be programmed to turn PMOS transistor 316 b ON, thereby setting node C′ high by passing V_(CC) through transistor 316 b, or power-up signal FCE 304 b of the pull-down circuit may be programmed to turn NMOS transistor 317 b ON, thereby setting node C′ low by passing V_(SS) through transistor 317 b, depending on which type of circuit the design called for. In all other cases, when both of FCEs 301 b and 302 b are programmed to turn ON transistors 314 b and 315 b, respectively, the pull-up circuit or pull-down circuit becomes inactive and node C′ is driven by routing signal 113 b via transistors 314 b and 315 b.

Unlike in the conventional receiver circuitry 300 a of FIG. 5 which requires a pull-up circuit, one benefit of receiver circuitry 300 b of the present invention is that a signal can be gated using a pull-up or a pull-down signal depending on the requirements of the design.

Once routing signal 113 b is passed by pass gates 314 b and 315 b to node C′ (or once node C′ is set HIGH by the pull-up circuit or set LOW by the pull-down circuit), the full-latch circuitry formed by inverters 313 b and 318 b brings the signal at node D′ to full-rail V_(CC) or V_(SS), whichever is substantially the inverse of the reduced or increased value of the signal at node C′. Therefore, whatever current leakage occurs due to the pass gates, the full-latch will set the signal at node D′ equal to the full-rail values of the supply voltage (i.e., V_(CC) or V_(SS)) albeit inverse full-rail values. Finally, inverter 319 b inverts the value of the signal at node E′. Therefore, whenever FCE 301 b is programmed to turn ON transistor 314 b and FCE 302 b is programmed to turn ON transistor 315 b, output terminal 320 b of receiver circuitry 300 b passes HIGH signal V_(CC) as destination signal 114 b to destination circuitry 20/30/40/100 when source signal 112 b is HIGH, and thus routing signal 113 b at node B′ is reduced-HIGH signal V_(CCN) (i.e., V_(CC)−V_(TN)). Also, whenever FCE 301 b is programmed to turn ON transistor 314 b and FCE 302 b is programmed to turn ON transistor 315 b, output terminal 320 b of receiver circuitry 300 b passes LOW signal V_(SS) as destination signal 114 b to destination circuitry 20/30/40/100 when source signal 112 b is LOW, and thus routing signal 113 b at node B′ is increased-LOW signal V_(SSP) (i.e., V_(SS)+V_(TP)). Yet, whenever one or both of FCEs 301 b and 302 b are not programmed to turn ON respective transistors 314 b and 315 b, output terminal 320 b of receiver circuitry 300 b either passes LOW signal V_(SS) as destination signal 114 b due to the pull-down circuit if provided, or passes HIGH signal V_(CC) as destination signal 114 b due to the pull-up circuit if provided, regardless of source signal 112 b.

Therefore, signal path circuitry 150 of the present invention drives a V_(CC) source signal 112 b via driver circuitry 200 b as a reduced-HIGH V_(CCN) routing signal 113 b along interconnection conductor 50/60/70/80/90, while receiver circuitry 300 b passes the reduced-HIGH V_(CCN) routing signal 113 b to source destination circuitry 20/30/40/100 as a full-rail V_(CC) destination signal 114 b. Similarly, signal path circuitry 150 drives a V_(SS) source signal 112 b via driver circuitry 200 b as an increased-LOW V_(SSP) routing signal 113 b along interconnection conductor 50/60/70/80/90, while receiver circuitry 300 b passes the increased-LOW V_(SSP) routing signal 113 b to source destination circuitry 20/30/40/100 as a full-rail V_(SS) destination signal 114 b. Thus, the voltage swing of routing signal 113 b driven along interconnection conductor 50/60/70/80/90 is not equal to the supply voltage of signal path circuitry 150 (i.e., V_(CC) to V_(SS)) but instead is limited to the range of V_(CCN) to V_(SSP).

FIG. 7 shows a detailed schematic diagram of a second embodiment of a reduced voltage swing signal path circuitry 160 according to the present invention. Signal path circuitry 160 includes “reversed” routing driver circuitry 200 b of FIG. 6 and routing receiver circuitry 300 c.

Each signal source element 20/30/40/100 in FIG. 7 can be similar to the signal source elements in FIGS. 2-6. The source of the signal in the signal path of circuitry 160 can be any of an I/O region 20, a logic region 30, a memory region 40, a programmable interconnection 100, or any other signal source on PLD 10. Routing driver circuitry 200 b is described above with respect to FIG. 6. Driver circuitry 200 b drives source signal 112 b onto a conductor that can be any of types 50, 60, 70, 80, or 90 or any other type of conductor used on PLD 10. The conductor 50/60/70/80/90 extending from driver circuitry 200 b runs to routing receiver circuitry 300 c. Each signal destination element 20/30/40/100 in FIG. 7 can be similar to the signal destination elements in FIGS. 2-6. Receiver circuitry 300 c passes the routing signal 113 c on conductor 50/60/70/80/90 as destination signal 114 c for application to the associated signal destination, which (like the signal source) can be any of an I/O region 20, a logic region 30, a memory region 40, a programmable interconnection 100, or any other signal destination on PLD 10.

As described above with respect to FIG. 6, output terminal 220 b of driver circuitry 200 b passes increased-LOW signal V_(SSP) (i.e., V_(SS)+V_(TP)) as a routing signal (i.e., routing signal 113 c with respect to signal path circuitry 150 of FIG. 7) to interconnection conductor 50/60/70/80/90. The routing driver circuitry 200 b functions as an inverter with a reduced voltage swing. The “HIGH” and “LOW” output levels at node B″ (and thus output terminal 220 b) equal V_(CCN) (i.e., V_(CC)−V_(TN)) and V_(SSP) (i.e., V_(SS)+V_(TP)), respectively. In other words, the voltage swing of routing driver circuitry 200 b is not equal to the supply voltage. Unlike in prior art driver circuitry 200 a of FIG. 5, the range of output voltages driven by routing driver circuitry 200 b as routing signal 113 c of FIG. 7 does not vary all the way between V_(CC) and V_(SS).

The routing signal 113 c driven onto interconnection conductor 50/60/70/80/90 is applied to routing receiver circuitry 300 c. Receiver circuitry 300 c passes routing signal 113 c on conductor 50/60/70/80/90 as destination signal 114 c for application to the associated signal destination, which (like the signal source) can be any of an I/O region 20, a logic region 30, a memory region 40, a programmable interconnection 100, or any other signal destination on PLD 10, similar to the signal destination elements in FIGS. 2-6.

In FIG. 7, routing signal 113 c from the interconnection conductor 50/60/70/80/90 is applied to the input terminal 312 c of routing receiver circuitry 300 c. V_(CC) is a source of power or logic 1 voltage or potential. V_(SS) is ground or logic 0 voltage or potential. Elements 314 c, 315 c, 317 c, and 318 c are NMOS transistors or gates and elements 313 c, 316 c, and 321 c are PMOS transistors or gates. Elements 301 c and 302 c are FCEs. Element 303 c is an active global signal (i.e., a power-up latch reset signal) that is LOW at power-up. Element 319 c is an inverter. Terminal 320 c is the output terminal of routing receiver circuitry 300 c. Elements 301 c and 314 c are all optional and can be omitted for any circuitry 300 c to speed up the device while increasing CRAM count on the PLD. NMOS transistor 315 c and FCE 302 c, together and in combination with optional NMOS transistor 314 c and FCE 301 c, form a pass gate. PMOS transistor 321 c in combination with power-up signal 303 c forms a “pull-up” circuit. PMOS transistors 313 c and 316 c in combination with NMOS transistors 317 c and 318 c form a low leakage input buffer.

Node C″ is formed between the drains of NMOS transistor 315 c and PMOS transistor 321 c, and between the gates of transistors 313 c and 316 c-318 c. The source of NMOS pass gate transistor 315 c is coupled to the drain of NMOS pass gate transistor 314 c. The source of NMOS pass gate 314 c is coupled to input terminal 312 c. Node D″ is formed between the drain of PMOS transistor 316 c, the source of NMOS transistor 317 c, and the input of inverter 319 c. Node E″, which is formed at the output of inverter 319 c, is connected to output terminal 320 c of circuitry 300 c. The gate of NMOS transistor 314 c is coupled to FCE 301 c and the gate of NMOS transistor 315 c is coupled to FCE 302 c. The drain of PMOS transistor 313 c is coupled to the source of PMOS transistor 316 c, while the drain of NMOS transistor 317 c is coupled to the source of NMOS transistor 318 c. The source of PMOS transistor 313 c is coupled to V_(CC), while the drain of NMOS transistor 318 c is coupled to V_(SS).

It will be understood that the drain and source orientation of the transistors described herein with respect to routing receiver circuitry 300 c is not intended to be limiting, but merely illustrative of one way such transistors can be constructed. Therefore, the terms “source” and “drain” are to be interpreted in their broadest sense.

Operation of receiver circuitry 300 c shown in FIG. 7 is as follows. When routing signal 113 c is a reduced-HIGH signal V_(CCN) (i.e., source signal 112 b is equal to V_(CC)), pass gates 314 c and 315 c pass reduced-HIGH routing signal 113 b to node C″ if FCEs 301 c and 302 c are programmed to turn ON transistors 314 c and 315 c, respectively. If either one or both of FCEs 301 c and 302 c is not programmed to turn ON its respective pass transistor (i.e., if FCE 301 c or FCE 302 c is LOW), then routing signal 113 c is not being driven to node C″ of receiver circuitry 300 c and, therefore, node C″ is floating. In that instance, which at least occurs when all FCEs are cleared (i.e., are LOW) at power-up of the programmable logic device on which circuitry 160 is contained, power-up signal 303 c of the pull-up circuit turns PMOS transistor 321 c ON, thereby setting node C″ HIGH by passing V_(CC) through transistor 321 c. In all other cases, when FCEs 301 c and 302 c are programmed to turn ON transistors 314 c and 315 c, respectively, node C″ is driven by routing signal 113 c via transistors 314 c and 315 c.

Unlike with respect to the other receiver circuitries previously described herein, after the pass gates of receiver circuitry 300 b there is no attempt to restore the signal at node C″ to full-rail using latch circuitry. Instead, input buffer circuitry is provided that can tolerate a low voltage swing at its input. When routing signal 113 c is passed by pass gates 314 c and 315 c to node C″, the input buffer circuitry formed by transistors 313 c and 316 c-318 c brings the signal at node D″ to substantially the inverse of the reduced or increased value of the signal at node C″, but at full-rail. Therefore, whatever current leakage occurs due to the pass gates, the low leakage input buffer will set the signal at node D″ equal to the HIGH (i.e., V_(CC)) or LOW (i.e., V_(SS)) values of routing signal 113 c, albeit inversed values. Finally, inverter 319 c inverts the value of the signal at node E″. Therefore, whenever FCES 301 c and 302 c are programmed to turn ON transistors 314 c and 315 c, respectively, output terminal 320 c of receiver circuitry 300 c passes HIGH signal V_(CC) as destination signal 114 c when source signal 112 b is HIGH, and thus when routing signal 113 c at node B″ is reduced-HIGH signal V_(CCN) (i.e., V_(CC)−V_(TN)). Also, whenever FCES 301 c and 302 c are programmed to turn ON transistors 314 c and 315 c, respectively, output terminal 320 c of receiver circuitry 300 c passes LOW signal V_(SS) as destination signal 114 c when source signal 112 b is LOW, and thus when routing signal 113 c at node B″ is increased-LOW signal V_(SSP) (i.e., V_(SS)+V_(TP)).

Therefore, signal path circuitry 160 of the present invention drives a HIGH V_(CC) source signal 112 b via driver circuitry 200 b as a reduced-HIGH V_(CCN) routing signal 113 c along interconnection conductor 50/60/70/80/90, while receiver circuitry 300 c passes the reduced-LOW V_(CCN) routing signal 113 c to source destination circuitry 20/30/40/100 as a full-rail HIGH V_(CC) destination signal 114 c. Similarly, signal path circuitry 160 drives a LOW V_(SS) source signal 112 b via driver circuitry 200 b as an increased-LOW V_(SSP) routing signal 113 c along interconnection conductor 50/60/70/80/90, while receiver circuitry 300 c passes the increased-LOW V_(SSP) routing signal 113 c to source destination circuitry 20/30/40/100 as a full-rail LOW V_(SS) destination signal 114 c. Thus, the voltage swing of routing signal 113 c driven along interconnection conductor 50/60/70/80/90 is not equal to the supply voltage of signal path circuitry 160 (i.e., V_(CC) to V_(SS)), but instead is limited to the range of V_(CCN) to V_(SSP).

Another benefit of receiver circuitry 300 c of FIG. 7 is that functionality issues are reduced with respect to routing across process corners within the logic device. For example, when the conventional signal path circuitry 140 of FIG. 5 is utilized in a signaling arrangement like illustrative signaling arrangement 130 of FIG. 4, routing driver circuitry 200 a is coupled to a large number of receiver circuitries, and therefore driver circuitry 200 a is coupled to a large number of half-latches via an equally large number of NMOS pass gates. It is to be understood that the NMOS pull-down transistor 216 a of driver circuitry 200 a must overcome the PMOS feedback transistor 317 a of each of the receiver circuitries 300 a utilized in the signaling arrangement. If too many PMOS feedback transistors 317 a coupled to driver circuitry 200 a are turned ON, or if the NMOS pull-down transistor 216 a is too weak due to process variation of the logic device, then the conventional signaling circuitry of FIG. 5 will fail to transition from V_(CC) to V_(SS). However, there is no feedback in receiver circuitry 300 c of reduced voltage swing signal path circuitry 160 of FIG. 7. Therefore, the maximum number of receiver circuitries 300 c that can be coupled to driver circuitry 200 b may be used without needing to simulate the functionality across all process corners.

Programmable logic device 10 constructed with any of the reduced voltage swing signal path circuitries described above may be used as part of a data processing system 500 shown in FIG. 8. Data processing system 500 may include one or more of the following components: a processor 501; memory 502; I/O circuitry 503; and peripheral devices 504. These components are coupled together by a system bus 505 and are populated on a circuit board 506, which is contained in an end-user system 507.

System 500 can be used in a wide variety of applications, such as computer networking, data networking, instrumentation, video processing, digital signal processing, or any other application where the advantage of using mask-programmable logic is desirable. Programmable logic device 10 can be configured to perform a variety of different logic functions. For example, logic device 10 can be configured as a processor or controller that works in cooperation with processor 501. Logic device 10 may also be used as an arbiter for arbitrating access to shared resources in system 500. In yet another example, logic device 10 can be configured as an interface between processor 501 and one of the other components in system 500. It should be noted that system 500 is only exemplary, and that the true scope and spirit of the invention should be indicated by the following claims.

Various integrated circuit process technologies can be used to implement logic devices 10 as described above according to this invention. In addition, other known signaling techniques such as low voltage differential signaling (LVDS) could be substituted for the single conductor signaling discussed in detail and still practice the principles of the invention.

It will be understood, therefore, that the foregoing is only illustrative of the principles of the invention, and that various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention, and the present invention is limited only by the claims that follow. 

1. A programmable logic device having programmable logic circuitry comprising: first operational circuitry; second operational circuitry; routing driver circuitry coupled to an output signal of the first operational circuitry; routing receiver circuitry coupled to an input of the second operational circuitry; and an interconnection conductor extending from the driver circuitry to the receiver circuitry, wherein the driver circuitry is configured to drive a routing signal onto the interconnection conductor, and wherein the voltage swing of the routing signal is less than the voltage swing of the output signal of the first operational circuitry.
 2. The programmable logic device of claim 1, wherein the voltage swing of the output signal of the first operational circuitry is defined by a first low signal and a first high signal, wherein the voltage swing of the routing signal is defined by a second low signal and a second high signal, and wherein at least one condition from the group consisting of the following is true: 1) the second low signal is higher than the first low signal, and 2) the second high signal is lower than the first high signal.
 3. The programmable logic device of claim 2, wherein the driver circuitry comprises a PMOS transistor coupled to an NMOS transistor.
 4. The programmable logic device of claim 3, wherein a base of the PMOS transistor and a base of the NMOS transistor are coupled to the output signal of the first operational circuitry.
 5. The programmable logic device of claim 4, wherein one condition from the group consisting of the following is true: 1) when the output signal of the first operational circuitry is defined by the first low signal, the PMOS transistor drives the second low signal onto the interconnection conductor as the routing signal, and 2) when the output signal of the first operational circuitry is defined by the first high signal, the NMOS transistor drives the second high signal onto the interconnection conductor as the routing signal.
 6. The programmable logic device of claim 2, wherein the receiving circuitry is configured to receive the routing signal from the interconnection conductor and to provide an input signal to the input of the second operational circuitry, wherein the voltage swing of the input signal to the second operation circuitry is defined by a third low signal and a third high signal, and wherein at least one condition from the group consisting of the following is true: 1) the second low signal is higher than the third low signal, and 2) the second high signal is lower than the third-high signal.
 7. The programmable logic device of claim 6, wherein the receiving circuitry comprises a full latch coupled to an inverter.
 8. The programmable logic device of claim 6, wherein the receiving circuitry comprises a low leakage input buffer coupled to an inverter.
 9. The programmable logic device of claim 6, wherein the receiving circuitry comprises a pull-up circuit.
 10. A digital processing system comprising: processing circuitry; a memory coupled to the processing circuitry; and a programmable logic device as defined in claim 1 coupled to the processing circuitry and the memory.
 11. A printed circuit board on which is mounted a programmable logic device as defined in claim
 1. 12. The printed circuit board defined in claim 11 further comprising: a memory mounted on the printed circuit board and coupled to the programmable logic device.
 13. The printed circuit board defined in claim 12 further comprising: processing circuitry mounted on the printed circuit board and coupled to the programmable logic device.
 14. A method of reducing power in a programmable logic device, the programmable logic device comprising first operational circuitry, second operational circuitry, routing driver circuitry coupled to an output signal of the first operational circuitry, routing receiver circuitry coupled to an input of the second operational circuitry, and an interconnection conductor extending from the driver circuitry to the receiver circuitry, the method comprising: driving a routing signal from the routing driver circuitry onto the interconnection conductor, wherein the voltage swing of the routing signal is less than the voltage swing of the output signal of the first operational circuitry.
 15. The method of claim 14, wherein the voltage swing of the output signal of the first operational circuitry is defined by a first low signal and a first high signal, wherein the voltage swing of the routing signal is defined by a second low signal and a second high signal, and wherein at least one condition from the group consisting of the following is true: 1) the second low signal is higher than the first low signal, and 2) the second high signal is lower than the first high signal.
 16. The method of claim 15, wherein the driver circuitry comprises a PMOS transistor coupled to an NMOS transistor.
 17. The method of claim 16, wherein the driving the routing signal comprises providing the output signal of the first operational circuitry to a base of the PMOS transistor and a base of the NMOS transistor.
 18. The method of claim 17, wherein one condition from the group consisting of the following is true: 1) when the output signal of the first operational circuitry is defined by the first low signal, the driving the routing signal further comprises the PMOS transistor driving the second low signal onto the interconnection conductor as the routing signal, and 2) when the output signal of the first operational circuitry is defined by the first high signal, the driving the routing signal further comprises the NMOS transistor driving the second high signal onto the interconnection conductor as the routing signal.
 19. The method of claim 15, wherein the receiving circuitry is configured to receive the routing signal from the interconnection conductor and to provide an input signal to the input of the second operational circuitry, wherein the voltage swing of the input signal to the second operation circuitry is defined by a third low signal and a third high signal, and wherein at least one condition from the group consisting of the following is true: 1) the second low signal is higher than the third low signal, and 2) the second high signal is lower than the third high signal.
 20. The method of claim 19, wherein the receiving circuitry comprises a full latch coupled to an inverter.
 21. The method of claim 19, wherein the receiving circuitry comprises a low leakage input buffer-coupled to an inverter.
 22. The method of claim 19, wherein the receiving circuitry comprises a pull-up circuit. 